1. Field of the Invention
The present invention relates to method and apparatus for transforming an image signal by a variable magnification factor.
2. Description of the Prior Art
In recent years, it has been proposed to read an original image of a text with an image sensor such as a CCD sensor, convert the read image to an electrical signal, digitize the electrical signal, and store in a memory or transmit the digitized image signal. When two images are combined and edited for printing or display, a dimension of an area in a first image in which a second image is to be inserted and a dimension of the second image to be inserted into the area of the first image are to be equal. If the dimension of the area into which the image is to be inserted and the dimension of the image to be inserted are different, either the area or the image to be inserted should be enlarged or reduced to make both dimensions equal and the digital signal of the magnified second image may be transferred to a memory area in which the digital signal of the first image signal is stored in order to combine both digital signals. In reproducing the combined image, the combined digital signal stored in the memory area is transferred to an output device such as a laser beam printer.
Where images of different dimensions are to be combined, it is necessary to change the dimension of the image without transforming a picture cell density.
On the other hand, where a facsimile device is connected to a computer output laser beam printer, the picture cell density must be transformed.
Facsimile devices usually have a picture cell density of 8 pixels/mm or 12 pixels/mm. On the other hand, most computer output laser beam printers have the picture cell density of 9.45 pixels/mm (240 pixels/inch). When an image signal transmitted through the 8 pixels/mm facsimile device is printed by the 9.45 pixels/mm laser beam printer, the image is reduced by a factor of 8/9.45 (=0.85). Thus, in order to produce a normal printout, the picture cell density must be transformed.
One method of transforming the picture cell density is to use a computer with appropriate software. However, this method is disadvantageous in that it takes a long time to magnify the image and transform the picture cell density because each of the picture cells must be processed. It may take several tens of seconds to several minutes even with a high performance computer.
In order to allow continuous magnification factor rather than fixed magnification factors such as factors of two and one-half, very complex software and peripheral hardware are required.
It is very difficult to variably magnify image data including half tone image data and no such proposal has been known.